Effect of Surface pH on Electrodeposited Ni Films

Ni metal was potentiostatically electrodeposited on a vertical plane cathode in a Watts bath in order to determine the effect of the cathode surface pH on the Ni film microstructure. Polarization curves and current efficiencies were measured at pH values of 1.5, 3.4, and 5.5. The surface pH value ( pH s ) was estimated from the measured partial current density for hydrogen gas evolution based on a steady-state one-dimensional mass transfer model. Any species relating to the buffering function through the dissociation reactions ( HSO 4 − , H 3 BO 3 , Ni 4 ( OH ) 4 4 + , H 3 O + , OH − ) were taken into account. The pH s abruptly rose to above 6 as the partial current density for H 2 gas evolution increased. The preferred orientation of electrodeposited Ni thin film was plotted in electrode potential- pH s diagram. It was found that the transition boundary between {110} and {100} preferred orientations was located along a ridge 500 mV below the H + ∕ H 2 equilibrium potential line. This relationship suggests that the dissolved hydrogen atoms in Ni metal are partly responsible for the evolution of structural texture of the Ni films.